NSW Police have launched an investigation after the body of an elderly man was found under a car at a farm north of Canberra.

Police were called to the property at Wallaroo, near the NSW-ACT border, shortly after midnight following the discovery of the 78-year-old man near a farm gate.

He is believed to be the property owner.

A crime scene has been established and an investigation is under way into the circumstances of the man's death, but a NSW Police spokesman said the homicide squad had not been called in.

"They've been advised as a matter of protocol it's an unexplained death," he said.

The man is yet to be formally identified.